1. Field of the Invention
The present invention relates to a tracking control apparatus for a disk recording medium, more particularly, to an apparatus of measuring how much an eccentricity affects each phase of a disk and controlling disk tracking based on the measured each effect rate.
2. Description of the Related Art
In general, most of the disks become eccentric during rotation because of variation in disk manufacturing or disk clamping condition. If an eccentricity of a disk is too high to conduct an exact tracking, it is difficult to reproduce data from the disk normally.
To overcome such a bad situation, a disk device measures an eccentricity of a disk and adjusts characteristic of a tracking servo to compensate the measured eccentricity at a start-up operation.
A conventional eccentricity measuring method rotates a placed disk with a tracking servo off, counts pulse train produced every track cross of an optical pickup and disk revolutions, and divides the pulse count by the number of disk revolutions. Because the value resulted from the division represents how much a disk is eccentric, gains of a tracking servo are adjusted based on the eccentricity measured as above to compensate eccentricity of the disk overall.
However, even though eccentricity of a disk is high, the high eccentricity has different effects on respective disk phases. Namely, a certain disk phase is affected less by the high eccentricity than other phases.
Nevertheless, if gains of a tracking servo are increased to make more sensitive to compensate an eccentricity overall irrespective of different effect of eccentricity on respective disk phases, a tracking servo may diverge unexpectedly, namely, an objective lens of an optical pickup may be biased to the utmost side when a scratch is encountered on a disk phase an eccentricity has small effect on.